Open back for better quality, closed back if you don't want to disturb others. AKG and Sennheiser are generally the names to look for, maybe something big enough to go over the ear rather than on it if you are going to be spending long periods listening to music.
http://www.whathifi.com/review/sennheiser-hd-202 Cheap and well recieved.
http://www.whathifi.com/review/sennheiser-px100-ii More expensive, slightly worse review!